Premixer array

The present disclosure relates to a premixer array for an engine. More particularly, the present disclosure relates to a premixer array including swirled premixers.

Conventional mixers for natural gas-powered turbine engines blend fuel with air to create a fuel-air mixture that is provided to a combustor of the engine. The conventional mixers mix inlet air and inlet fuel to create the fuel-air mixture. The inlet air may be introduced to the combustor without imparting a swirl.

According to an embodiment, a premixer array for a combustion section of a gas turbine engine includes one or more pilot tubes configured to cause a pilot product to flow and a plurality of swirled premixer tubes. The plurality of swirled premixer tubes being configured to guide and to spread out the pilot product in a radial direction, in a circumferential direction, or both in the radial direction and the circumferential direction.

According to an embodiment, a premixer array for a combustion section of an engine includes a plurality of swirled premixer tubes having one or more tangential openings and being configured for providing a swirled flow to a fuel-air mixture therethrough. The premixer array further includes one or more non-swirled premixer tubes omitting the one or more tangential openings and being configured for providing a non-swirled flow to a fuel-air mixture therethrough. The swirled flow is in a clockwise direction when the one or more tangential openings are angled in a clockwise direction or in a counterclockwise direction when the one or more tangential openings are angled in a counterclockwise direction.

According to an embodiment, a method of controlling a flow of pilot products from a pilot tube includes providing an opposed fuel-air mixture flow from a clockwise fuel-air mixture flow and a counterclockwise fuel-air mixture flow in a mixer array, providing a flow of pilot products in the mixer array, guiding, with the opposed fuel-air mixture flow, the flow of pilot products in a radial direction, in a circumferential direction, or in both a radial direction and a circumferential direction, and spreading, with the opposed fuel-air mixture flow, the flow of pilot products.

Additional features, advantages, and embodiments of the present disclosure are set forth or apparent from a consideration of the following detailed description, drawings, and claims. Moreover, it is to be understood that both the foregoing summary of the disclosure and the following detailed description are exemplary and intended to provide further explanation without limiting the scope of the disclosure as claimed.

Various embodiments are discussed in detail below. While specific embodiments are discussed, this is done for illustration purposes only. A person skilled in the relevant art will recognize that other components and configurations may be used without departing from the spirit and scope of the present disclosure.

The premixer arrays of the present disclosure provide combinations of co-flowing premixers and counter-flowing premixers to control the direction of flow of pilot products. In some examples, premixers with counterclockwise swirl may be placed adjacent to premixers of clockwise swirl to guide the pilot products radially and/or circumferentially. In some examples, a subset of premixers may guide the pilot products. In some examples, the premixers may guide the pilot products to nearby premixers or adjacent (e.g., directly next to) premixers. The direction of swirl may be achieved by angling the tangential openings of the premixer in a counterclockwise manner or a clockwise manner. The arrangement of premixers may be selected within a premixer zone, between adjacent premixer zones, between adjacent premixer arrays, between multiple premixer arrays, or any combination thereof.

shows an enginehaving a mixer. The enginemay be, for example, a gas turbine engine. The mixermay include a plurality of premixersarranged in one of a plurality of premixer arrays. The mixermay be configured to facilitate mixing of an air flow and a fuel flow through the enginefor providing to a combustion sectionhaving a combustion linerthat includes an inner linerand an outer liner. A bulkhead wallof the combustion sectionextends between the inner linerand the outer liner. Each of the premixer arraysincludes a premixer array mounting platecoupled to the bulkhead wall. Although eleven premixersare shown in each premixer array, more or fewer may be provided. Only a portion of the engineand mixerare shown and it may be understood that the engineand mixerare revolved around a centerline, such that the mixertakes a generally annular or donut shape and the plurality of premixer arraysis arranged in a circumferential direction of the mixer.show views of one the plurality of premixer arrays. Each of the premixer array mounting platesof the plurality of premixer arraysdefines a plurality of tube portsextending therethrough. The plurality of premixersof each of the plurality of premixer arraysmay be placed within (or coupled to) the plurality of tube ports. The premixersof the premixer arraymay be divided into zones, such as an A-Zone, a B-Zone, and a C-Zone, as shown in. As shown in, the plurality of tube portsof the premixer array mounting platemay extend in each of the A-Zone, the B-Zone, and the C-Zone.

andshow exemplary premixersfor use in the premixer arrayof. With reference to, the premixermay be a swirled premixer tube. The swirled premixer tubemay include a plurality of tangential slots. The tangential slotsmay be angled to provide the flow direction in the flow therethrough the swirled premixer tube. That is, the tangential slotsmay be angled to provide a clockwise direction flow CW (see, for example,) or a counterclockwise direction flow CCW (). As shown in, the tangential slotsmay be angled in a counterclockwise direction to impart the counterclockwise direction flow CCW. As shown in, the tangential slotsmay be angled in a clockwise direction to impart the clockwise direction flow CW. The degree to which the tangential slotsare angled with respect to a normal axis through the swirled premixer tubemay be selected based on the desired flow therethrough. The swirled premixer tubemay impart flow direction and turbulence to the flow therethrough.

Referring to, the premixermay be a non-swirled premixer tube. The non-swirled premixer tubemay omit the tangential slotsof. Thus, the flow through the non-swirled premixer tubemay not be intentionally directed in a clockwise direction or a counterclockwise direction. Any combination of swirled premixer tubesand non-swirled premixer tubesmay be provided in each premixer arrayof the mixer, as will be described in the following disclosure.

Providing swirled premixer tubesin the premixer arraymay provide flame stability to various zones (e.g., A-Zone, B-Zone, and/or C-Zone) of the premixer array, may create a shear layer between adjacent premixers, which may achieve enhanced mixing (as compared to non-swirled premixers) and lower NOemissions, and may create a secondary flow structure (e.g., a swirling flow), that may help to reduce combustion dynamics. Including swirled premixer tubesin the premixer arraymay reduce or eliminate circumferential flow within the mixer.

toshow exemplary arrangements of swirled premixer tubesand non-swirled premixer tubeslocated in the couplets of the premixer array. Any combination of clockwise swirled premixer tubes, counterclockwise swirled premixer tubes, and non-swirled premixer tubes may be provided in the premixer arraysof the present disclosure based on the desired flow and mixing through the engine(). Although a single premixer arrayis shown in some examples, a plurality may be provided such as shown in. The premixer arraysofmay include one or more of the exemplary arrangements described into, in any combination (e.g., all the same array, all different arrays, mixes of multiple arrays, etc.).

Referring now to, a premixer arraymay include a plurality of non-swirled premixer tubesand a plurality of swirled premixer tubes. The swirled premixer tubesmay include clockwise swirled premixer tubesand counterclockwise swirled premixer tubes. That is, the tangential openingsmay be arranged in a clockwise direction (clockwise swirled premixer tubes) and the tangential openingsmay be arranged in a counterclockwise direction (counterclockwise swirled premixer tubes). Thus, the tangential openingsmay impart a clockwise swirl on the flow therethrough and the tangential openingsmay impart a counterclockwise swirl on the flow therethrough.

The premixer arrayofmay include a pilot tube. The pilot tubemay provide a fuel flow to the mixer(). The fuel flow may be a gas fuel or a liquid fuel, or a combination thereof. The swirled premixer tubesand the non-swirled premixer tubesmay provide an air flow to the mixer(). Thus, the mixermay provide a fuel-air mixture (provided by the combination of air flow from the premixersand the pilot tube(s)) to the engine().

In operation, and with particular reference to, a fuel flow may be provided through the pilot tube. The pilot tubemay be a swirling tube or a non-swirling tube. At the exit of the pilot tube, the fuel flow may interact with an air-fuel mixture flow from the swirled premixer tubes.shows a subset of swirled premixer tubesthat form a square in plan view. The pilot tubemay be located at a center of the square in plan view and, thus, at a center of the subset of swirled premixer tubes.

As shown in, the swirled premixer tubeson the top side ofin the B-Zone may be arranged such that the top right premixer is a clockwise swirled premixer tubeand the top left premixer is a counterclockwise swirled premixer tube. This may generate a combined premixer fuel-air mixture flow that acts to move the pilot fuel or fuel-air mixture flow or pilot products to flow in a radial outward direction R (e.g., in a radial direction with respect to the engineof. This may also be referred to as an axial direction of the premixer array) to provide a flow() of fuel-air mixture or combustion products in the radially outward direction and radially inward direction. A similar action is achieved on the bottom side ofin the B-Zone by arranging the bottom left premixer as a counterclockwise swirled premixer tubeand the bottom right premixer as a clockwise swirled premixer tube. This arrangement may cause pilot products to move radially inward in the direction R. Thus, when two adjacent premixers are arranged with opposing flows (e.g., one arranged clockwise and one arranged counterclockwise), the fuel-air mixture flow from the premixer may meet and pull the pilot fuel or fuel-air mixture flow or products of combustion from pilot along therewith. That is, adjacent swirled premixer tubesmay be arranged to flow in opposing directions. The adjacent swirled premixer tubesmay be arranged to cause the pilot products to flow in a radially outward direction and/or a radially inward direction. Thus, as shown in, the top two premixers of the B-Zone pulls the fuel flow radially outward and the bottom two premixers of the B-Zone pulls the fuel flow radially inward. Such an arrangement may reduce or prevent circumferential flow of the pilot fuel or combustion product from pilot (e.g., fuel or pilot combustion product to the left and right as viewed in) and induce the combustion products from pilot to move towards A-Zone or C-Zone thereby providing flame stability to the premixers in A-Zone and C-Zone that do not have a pilot. Including a swirled premixer in the C-Zone may further pull the now fuel-air mixture in the desired direction. Although shown inas a clockwise swirled premixer tube, this may be a counterclockwise swirled premixer tube. A swirled premixer tube provided in the C-Zone or in the upper A-zone may assist in reducing a re-circulation zone closer to the combustion liner(), which is typically seen with non-swirling premixer. Reducing the corner re-circulation zone closer to the combustion linerhelps in reducing flame quenching effect and maintaining a shortened flame for premixers those are near the inner liner or the outer liner of the combustion zone.

Accordingly, the opposing flow of the swirled premixer tubesmay move the pilot products in a selected direction or a predetermined direction. This arrangement may be used to induce the pilot products to flow from the pilot tube to the main mixer and, thus, to the engine. Directing the pilot products in the desired direction may allow for the premixer arrayto achieve enhanced mixing and lower NOemissions as compared to premixer arrays that do no employ such directing of pilot products. As shown in, the pilot products are induced to flow radially towards A-Zone and C-Zone and circumferential flow is limited.

Referring now to, a premixer arraymay include a plurality of non-swirled premixer tubesand a plurality of swirled premixer tubes. The swirled premixer tubesmay include clockwise swirled premixer tubesand counterclockwise swirled premixer tubes. The arrangement in the B-Zone and the C-Zone of the premixer arrayofmay be the same as in the premixer arrayof. Additionally, the premixer arrayof, may include swirled premixer tubesin the A-Zone. The top two premixers in the A-Zone may be swirled premixer tubes. The swirled premixer tubesin the A-Zone may be arranged in opposing flows, e.g., one clockwise swirled premixer tube(on the right in) and one counterclockwise swirled premixer tube(on the left in). The addition of swirled premixer tubesin the A-Zone may reduce the corner circulation zone and may prevent flame straining. That is, the swirled premixer tubesin the A-Zone may cause the premixer products closer to the periphery to flow in the direction R to clear the recirculation zone. The addition of swirled premixer tubesin the C-Zone may maintain a shorter flame near the combustion liner(). The addition of swirled premixer tubesin the B-Zone may induce pilot products from the pilot tubeto flow in the direction R toward the A-Zone and to, for example, the fifth premixer in the B-Zone (e.g., the non-swirled fifth premixer tube).

shows an exemplary arrangement of swirled premixer tubes, non-swirled premixer tubes, and pilot tubesin a premixer array. In, the A-Zone may include a pilot tubeand opposing clockwise swirled premixer tubesand counterclockwise swirled premixer tubes. The arrangement in the A-Zone may be the same as or similar to the arrangement of the B-Zone in. Additionally, in the B-Zone, a pilot tubemay be provided in conjunction with a clockwise swirled premixer tubeand a counterclockwise swirled premixer tube. In the C-Zone, a clockwise swirled premixer tubemay be included, although a counterclockwise swirled premixer tube may alternatively be selected.

The arrangement ofprovides the B-Zone swirled premixer tubesthat may induce the pilot tubeflow in the B-Zone to flow in the direction R to the fifth premixer tubein the B-Zone. The A-Zone swirled premixer tubesmay induce the product of pilot tubein the A-Zone to flow to the A-Zone main tubes and to the periphery to reduce and/or to clear the recirculation zone. The C-Zone swirled premixer tubemay maintain a shorter flame near the combustion liner by reducing corner re-circulation zone near liner and thereby flame straining.

shows an exemplary arrangement of swirled premixer tubes, non-swirled premixer tubes, and pilot tubesin a premixer array. In, the A-Zone may include opposing clockwise swirled premixer tubeand counterclockwise swirled premixer tube. The swirled premixer tubesin the A-Zone may be provided in the lower portion of the A-Zone. The arrangement in the B-Zone may be the same as or similar to the arrangement of the B-Zone in. In the C-Zone, a clockwise swirled premixer tubemay be included, although a counterclockwise swirled premixer tube may alternatively be selected.

The arrangement ofprovides the B-Zone swirled premixer tubesthat may induce the pilot tubein the B-Zone to flow in the direction R toward the A-Zone and in the direction R toward the fifth premixer tube. The swirled premixer tubesin the lower A-Zone may move the pilot product from the B-Zone pilot tubein the direction R toward the outermost A-Zone main mixer. The C-Zone swirled premixer tubemay maintain a shorter flame near the combustion liner and may fight or reduce near-wall recirculation.

shows an exemplary arrangement of swirled premixer tubes, non-swirled premixer tubes, and pilot tubesin a premixer array. In, the arrangement in the A-Zone and the arrangement in the B-Zone may be the same as or similar to the arrangement of the B-Zone in. In the A-Zone, the liquid pilot tubemay be a liquid pilot and the gas pilot tubemay be a gas pilot. In the C-Zone, a clockwise swirled premixer tubemay be included, although a counterclockwise swirled premixer tube may alternatively be selected.

The arrangement ofmay include a liquid pilot tubein the A-Zone. The swirled premixer tubesin the A-Zone may induce the liquid pilot products to flow toward the A-Zone main mixer. The swirled premixer tubesin the A-Zone may also reduce a corner circulation zone and prevent flame straining. The swirled premixer tubesin the B-Zone may induce the gas pilot tubein the B-Zone to flow in the direction R toward the A-Zone and in the direction R toward, for example, the fifth premixer tube. The C-Zone swirled premixer tubemay maintain a shorter flame near the combustion liner and may fight or reduce near-wall recirculation. In the arrangement of, the liquid pilot tubeand the gas pilot tubemay be operated at different time periods. The location of the liquid pilot tube, although shown in the A-Zone, may be in the B-zone and/or may be in-between the B-Zone and the C-Zone. The gas pilot tube, although shown in the B-Zone, may be in the A-Zone and/or in-between the A-Zone and the B-Zone.

shows an exemplary arrangement of swirled premixer tubes, non-swirled premixer tubes, and pilot tubesin a premixer array. In, the arrangement of the B-Zone may be the same as or similar to the arrangement of the B-Zone in. In the A-Zone, a pilotmay be included. In the C-Zone, a clockwise swirled premixer tubemay be included, although a counterclockwise swirled premixer tube may alternatively be selected.

The arrangement ofprovides the B-Zone swirled premixer tubesthat may induce the pilot tubeflow in the B-Zone to flow in the direction R toward the A-Zone and in the direction R toward, for example, the fifth premixer tube. The pilotin the A-Zone adds pilot products to the flow and is induced radially outward in the direction R by the B-Zone arrangement. The C-Zone swirled premixer tubemay maintain a shorter flame near the combustion liner.

shows an exemplary arrangement of swirled premixer tubes, non-swirled premixer tubes, and pilot tubesin a premixer array. In, the arrangement of the B-Zone may be the same as or similar to the arrangement of the B-Zone in. In the A-Zone, a pilotmay be included. The A-Zone may also include a pair of opposed direction swirled premixer tubesin the upper portion (e.g., in the upper couplets) of the A-Zone. In the C-Zone, a clockwise swirled premixer tubemay be included, although a counterclockwise swirled premixer tube may alternatively be selected.

The arrangement ofprovides the B-Zone swirled premixer tubesthat may induce the pilot tubein the B-Zone to flow in the direction R toward the A-Zone and in the direction R toward, for example, the fifth premixer tube. The A-Zone swirled premixer tubesmay induce the product of pilot tubein the A-Zone and the B-Zone to flow to the A-Zone main tubes and to the periphery to reduce and/or clear the recirculation zone. The C-Zone swirled premixer tubemay maintain a shorter flame near the combustion liner().

shows an exemplary arrangement of swirled premixer tubes, non-swirled premixer tubes, and pilot tubein a premixer array. In, the arrangement spanning the lower couplets of the A-Zone and the upper couplets of the B-Zone may be the same as or similar to the arrangement of the B-Zone in. The arrangement ofshows the pilot tubeplaced in-between the A-Zone and the B-Zone and provides swirled premixer tubesin the A-Zone that induce the product of pilot tubeto flow to the A-Zone main tubes in the direction R and to the lower couplets in the B-Zone in the direction R.shows a similar arrangement as that shown inwith the addition of a swirled premixer tubein an upper couplet of the C-Zone.

show exemplary arrangements of adjacent premixer arrays. In the premixer arraysof, adjacent premixersmay be arranged in a clockwise swirled premixer tubeand counterclockwise swirled premixer tubeopposed relationship. This opposed relationship may function as previously described to pull the pilot products in a predetermined direction.

In the example of, the pilotsmay be located between adjacent premixer arrays. The swirled premixer tubeslocated on the right hand side of the left premixer arraymay interact with the pilot products to move the products in the direction R, as described previously. Similarly, the swirled premixer tubeslocated on the left hand side of the right premixer arraymay interact with the pilot products to move the products in the direction R, as described previously. The pilot tubeintroduced in between two adjacent premixer arraysmay cause the pilot combustion products to flow towards the main mixer of an adjacent premixer assembly or to a premixer array for flame stability. The pilot products may flow in the radial direction.

In the example of, the pilotsmay be located between adjacent premixer arrays. The swirled premixer tubeslocated on the right hand side of the left premixer arraymay interact with the pilot products to move the products in the direction C, e.g., circumferentially around the mixer(). Similarly, the swirled premixer tubeslocated on the left hand side of the right premixer arraymay interact with the pilot products to move the products in the direction C, as described previously. The pilot tubeintroduced in between two adjacent premixer arraysmay cause the pilot combustion products to flow towards the main mixer of adjacent premixer assembly or to a premixer cup for flame stability. The pilot may flow in the circumferential direction.

In the example of, the pilotsmay be located between adjacent premixer arrays. The swirled premixer tubesmay be arranged such that one or more sets of the swirled premixer tubespull the pilot products in a circumferential direction C and one or more sets of the swirled premixer tubespull the pilot products in a radial direction R. For example, premixer array, premixer array, and the left side swirled premixer tubesof premixer arraymay be arranged such that these premixers pull the combustion products from the pilot tubecircumferentially in the direction C toward a central pilot tube. Similarly, the premixer array, premixer array, and the right side swirled premixer tubesof premixer arraymay be arranged such that these premixers pull the combustion products from the pilot tubecircumferentially in the direction C toward the central pilot tube(e.g., in a circumferentially opposite direction as premixer array, premixer array, and premixer array). The right side swirled premixer tubesof premixer arrayand the left side swirled premixer tubesof premixer arraymay pull the combustion products from the circumferential flow and from the central pilot tubein a radial direction R. A similar arrangement may be provided with the swirled premixer tubesspanning the B-Zone and the C-Zone to pull the combustion products in a circumferential direction C.

The arrangement ofmay provide a combination of a radial flow direction and a circumferential flow direction of pilot combustion products induced by a combination of a co-flowing main mixer and a counter-flowing flowing main mixer may improve flame propagation and flame stability. The pilot for radial flow may be situated between main mixers of adjacent premixer assemblies. The products of combustion are further extended circumferentially towards a second premixer assembly to the right and/or the left from the pilot location. The products of combustion then flow radially between adjacent premixer assemblies.

show an example of adjacent premixer arrays. As shown, the pilot tubesmay be provided between adjacent premixer arrays(e.g., between premixer arrayand premixer array, between premixer arrayand premixer array; and/or between premixer arrayand premixer array). The pilot tubesmay also be provided within a premixer array(e.g., within premixer arrayand premixer array). The arrangement of clockwise swirled premixer tubesand counterclockwise swirled premixer tubesmay induce flow of the pilot products circumferentially in the direction C, radially in the direction R, or both circumferentially and radially. The combination of a radial flow direction and a circumferential flow direction of pilot combustion products induced by the combination of a co-flowing main mixer and a counter-flowing main mixer may improve flame propagation and flame stability. The pilot for radial flow may be situated between main mixers of the same premixer assembly. The products of combustion flow radially between adjacent main mixers of the same premixer assembly.

show exemplary mixer arrays for an annular combustor. Referring first to, an annular combustoris shown with a mixer arrayincluding a plurality of mixersand a pilot tube. Althoughshows an arrangement of four mixersand one pilot tube, the mixer arraymay extend annularly around the combustor, such as is described in.

shows an exemplary mixer arrayfor an annular combustor(). The annular combustormay include an outer linerand an inner liner. The mixer arraymay include a plurality of swirled premixer tubes. The swirled premixer tubes, such as clockwise swirled premixer tubesand counterclockwise swirled premixer tubesmay be arranged between the inner linerand the outer liner. The mixer arraymay include one or more pilot tubes(which may be the same as pilot tube). As described previously, the swirled premixer tubesmay be arranged to pull the pilot products circumferentially in the direction C and/or radially in the direction R. The arrangement ofallows the circumferential spread of hot products from the pilot tubeto adjacent main tubes. The arrangement ofmay improve circumferential flame propagation.

In, the mixer arraymay include swirled premixer tubesarranged to pull the pilot products from the pilot tubein a radial direction R toward an ignitor. This may allow for the pilot flow to be pushed toward the ignitorto assist or to enhance ignition.

In, the mixer arrayallows for the elimination of every other pilot tube. The ability of the swirled premixer tubesto be arranged to provide circumferential flow in the direction C allows for alternate pilot tubes to be omitted or eliminated. This occurs because the arrangement creates central couplets to drive the pilot products toward the center. This reduces the total number of pilot tubesrequired in the premixer array.

For example,may include a first subset of premixer tubes, a second subset of premixer tubes, and a third subset of premixer tubes. Each of the subset of premixer tubes may include four swirled premixer tubes arranged in the manner shown in. Each of the first subset of premixer tubesand the third subset of premixer tubesmay include a pilot tube. The second subset of premixer tubesmay not include a pilot tube. The first subset of premixer tubesmay extend and spread the pilot flow from the pilot tubein a circumferential direction beyond the first subset of premixer tubesand into the adjacent second subset of premixer tubes. Similarly, the third subset of premixer tubesmay extend and spread the pilot flow from the pilot tubein a circumferential direction beyond the third subset of premixer tubesand into the adjacent second subset of premixer tubes. This pattern may be repeated about the annular combustor(). The second subset of premixer tubesmay be adjacent and in-between the first subset of premixer tubesand the third subset of premixer tubes. In this manner, the required flame propagation for operation of the combustor may be achieved with fewer pilots, as every other pilot tubemay be omitted.

In, the mixer arrayallows for the limitation of two of every four pilot tubes. Each pilot tubesfeeds two adjacent main couplets. The ability of the swirled premixer tubesto be arranged to provide circumferential flow in the direction C allows for the pilot tubes to be omitted or eliminated.

The mixer arrays described herein may be provided in a variety of arrangements to achieve a desired flow direction of each mixer array or of multiple mixer arrays. For example, the premixer array may include a first premixer array and a second premixer array. The first premixer array may produce a clockwise flow and the second premixer array may produce a counterclockwise flow. That is, the premixer array may include two or more premixer arrays, wherein half of the two or more premixer arrays produce a clockwise flow and one of the two or more premixer arrays produces a counterclockwise flow. For example, where two mixer arrays are present, one premixer array has a clockwise flow and one premixer array has a counterclockwise flow, when four premixer arrays are present two premixer arrays form a clockwise flow and one premixer array forms a counterclockwise flow, and so on.

Accordingly, the premixer array of the present disclosure provides for a pilot introduced between main mixer swirl couplets to provide enhanced radial spread of product of combustion from pilot tubes to flow towards both upper sides and lower sides of the main mixer cluster or tubes. Upward (e.g., radially outward) pilot flow may be induced using a combination of clockwise left swirler tubes and anticlockwise (or counterclockwise) right swirler tubes. Downward (e.g., radially inward) pilot flow may be induced using a combination of counterclockwise left swirler tubes and clockwise right swirler tubes. This may provide stable ignition source to main tubes or a cluster of main tubes. Circumferential flow may be eliminated in some examples. The direction of flow of the pilot products may be controlled by placement of the swirled premixer tubes and by selection of counterclockwise or clockwise angled tangential openings in the premixer tubes.

According to the present disclosure, the premixer arrays may reduce a recirculation zone, reduce temperature of the liner, stabilize the flame structure, move the flow closer to the outer liner to fill the recirculation zone, and/or move the flow closer to the inner liner to reduce the temperature on the liner.

According to the present disclosure, a combination of clockwise and counterclockwise, lightly swirled premixer tubes may create a secondary flow structure that positively impacts the heat release near the dome and heat shield, which may provide a combustion dynamics benefit.

According to the present disclosure swirl couplets (e.g., swirled premixer tubes) may be provided close to an outer liner and/or inner liner of the combustion zone to reduce a corner circulation zone near the liner. This may reduce flame quenching, may lower CO emissions, and may lower the liner temperature.

According to the present disclosure, a swirling pilot and/or a non-swirling pilot may be introduced between non-swirling premixer tubes or swirling premixer tubes to cause products of combustion from the pilot to flow toward adjacent premixer tubes or adjacent clusters of premixer tubes or adjacent premixer arrays. This may provide enhanced flame stability.

According to the present disclosure, couplets (e.g., premixer tubes) may be put on any row and/or column of the premixer array and/or between adjacent premixer zones (e.g., between the A-Zone and the B-Zone, or the A-Zone, or the B-Zone) and/or between adjacent premixers.

According to the present disclosure, a pilot flame temperature may be maintained the same as the main tubes at higher power mode to achieve a lower emission. The pilot flame temperature may be maintained at 50° F. to 500° F. higher than the main flame temperature to achieve better operability at lower power modes.